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Discovery of the world’s highest-dwelling mammal
March 15, 2021

Yellow-Rumped Leaf-eared Mouse (Phyllotus xanthopygus, photo credit Marcial Quiroga-Carmona)


Article Details:


Storz, J. F. M. Quiroga-Carmona, J. C. Opazo T. Bowen, M. Farson, S. J. Steppan, and G. D’Elía. 2020. Discovery of the world’s highest-dwelling mammal. Proceedings of the National Academy of Sciences117:18169-18171.

This posting highlights a spectacular discovery, recently reported in one of the world’s most prestigious periodicals. Back in 2005, concerned about dwindling support for natural history, I noted that “Theories summarize science, tell us what to measure when we test hypotheses, and help us study nature better. Nevertheless, organisms themselves embody genetics, development, morphology, physiology and behavior; they are the units of populations, communities and ecosystems. Biologists seek to understand organisms, their diversification and environmental relationships—not theories and experiments per se—and discoveries of new organisms and new facts about organisms reset the research cycles of hypothesis testing that underlie conceptually progressive science” (Trends in Ecology and Evolution 20, p. 23; for a pdf of the article, write to Now natural history is once again flourishing, exemplified by American Naturalist, Ecology, Proceedings of the National Academy of Sciences, and other high impact journals featuring primarily descriptive studies among their more theory-oriented contributions.

Jay Storz is a distinguished University of Nebraska professor, an expert on adaptations to extreme environments, and a biologist as at home in the field as in the laboratory. Jay’s many publications include a new book on hemoglobin, the molecule in blood that carries oxygen to our tissues; he’s also an experienced backpacker, as I learned years ago when we hiked for several days together in the Grand Canyon. In 2019, while on sabbatical leave in Argentina, Jay was contacted by two climbers who had video of a mouse scurrying across snow at 6,205 m (20,358 ft) on Volcán Llullaillaco. He had long been fascinated by mountaineer sightings of high-altitude animals, such as geese flying overhead near the summit of Mount Everest (8,849 m, 29,032 ft). He also knew that the highest mammal vouchered by a museum specimen was a Large-eared Pika (Ochotona macrotis, a rabbit relative), from 5,182 m (17,001 ft) in the Himalayas, and that a 1921 Everest expedition reported credible sightings of that same species at 6,130 m (20,112 ft).

The world’s second highest active volcano, Llullaillaco straddles the Argentina-Chile border and towers above the Atacoma Desert, which lies between it and the Pacific Ocean. As Jay explained to me in an email, “After seeing that mouse video, it didn’t take long to decide that I needed to get down there. So I organized an international team of friends from the Universidad Austral de Chile, with members from Uruguay, Bolivia, and Venezuela, as well as Chile and the U.S. In February of 2020, we trapped mice over a range of elevations in the Puna de Atacama in northern Chile, including a surprising number at our base camp at 5,070 m (16,634 ft). Despite MUCH effort, we did not catch any around our high camp at 5,850 m (19,193 ft), where storms later in the day often buried our traps beneath snow and ice.”

What followed reads like a classic moment in exploratory natural history, something straight out of Alexander von Humboldt or Alfred Russel Wallace. As Jay tells it, “When my friend Mario and I set off on our summit attempt, towards the very end of our trip, I planned to search for tracks and burrows but wasn’t expecting live animals. We were fortunate to have really good weather, and the summit itself was mostly snow-free. Mario first saw the mouse. I was pretty gassed, as we had been climbing continuously since leaving our tent in the high camp at 2 AM, but when my oxygen-deprived brain finally processed what Mario was telling me, I quickly came to my senses. Experience from a youth spent catching lizards came in handy!” At 6,739 m (22,110 ft), Jay had just hand-captured the highest ever recorded native mammal, a Yellow-rumped Leaf-eared Mouse (Phyllotus xanthopygus).

Along with the summit mouse, Jay and his collaborators collected more than a hundred others as museum vouchers at their camps, all now curated at Universidad Austral de Chile for further study. From those specimens they also stored tissues for later DNA sequencing and analyses, and thus proved that their top of the world rodents pertain to four known species—of which P. xanthopygus has an altitudinal range unprecedented among mammals, from sea level to Llullaillaco’s peak. As the authors noted, this raises all sorts of unexpected questions, just as I’d predicted would generally be the case in my editorial defense of natural history. What do the mice eat, for example, since they thrive more than 2,000 m above the limits for green plants? Meanwhile, the Storz et al. report is open access and accessible to lay readers; anyone may access it via the above link, and therein view videos of the first mouse sighting (Movie S1) and of Jay’s summit capture (Movie S2). 

Meet Harry Greene

Harry W. Greene is emeritus professor of ecology and evolutionary biology at Cornell University, author of Snakes: The Evolution of Mystery in Nature and Tracks and Shadows: Field Biology as Art, and a member of the NHI’s science advisory council.
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